A fiber reinforced plastic molded component composed of a continuous reinforcing fiber such as a carbon fiber, glass fiber and aramid fiber, and a cured material of a matrix resin such as an epoxy resin, unsaturated polyester resin, vinyl ester resin and phenol resin shows excellent mechanical properties of strength, elastic modulus, impact resistance and fatigue resistance, and also has a characteristic of being light in weight, so that it is widely used in applications such as aviation, space, sport, automobile, marine vessel, home electric appliance, civil engineering and construction.
In production of the fiber reinforced plastic molded component, there is often used a method where a prepreg, a sheet-like intermediate material in which an uncured thermosetting resin is impregnated in a fabric substrate constituted by a continuous reinforced fiber, is laid up on a molding tool, then pressurized/heated in an autoclave. However, the uncured thermosetting resin impregnated in a prepreg has generally a high viscosity, and the relative position of reinforcing fiber bundles constituting a fabric substrate is constrained by the resin impregnated. Therefore, the prepreg has a high rigidity and low deformability, bad in following a mold and difficult to shape into a three-dimensional shape. This is one cause for hamper of production improvement.
To the above-described problem, an infusing molding method has recently been paid attentions as a method for improving productivity, which is typified by RTM (Resin Transfer Molding) where a reinforcing fiber substrate that a matrix resin is not impregnated in beforehand (so-called dry) is positioned inside a molding tool, then, by infusing a liquid matrix resin with low viscosity, the matrix resin is impregnated in the reinforcing fiber substrate, and cured after that.
In the infusing molding method, generally, it takes procedures where a dry reinforcing fiber substrate that a matrix resin is not impregnated in is laid up on a molding tool so that it follows a shape of mold, which is next covered by a vacuum bagging film or a molding tool, then, a resin is infused therein and cured. Since a dry reinforcing fiber substrate is used in this method, deformability is large and it follows well a three-dimensional shape. However, on the other hand, there is a problem that shape retention is bad, laying-up operations take time, occupying an expensive molding tool for a long time.
To more improve productivity beyond the above-described problems, there is also proposed a method that a laying-up process of reinforcing fiber substrates and an infusion process of resin are separated. Namely, first, it is provided with a shape (near-net-shape), i.e., substantially the same shape as the case of laying up dry reinforcing fiber substrates on a molding tool, and a so-called preform retaining the shape is formed. Thereafter, the preform is placed on a molding tool, in which a matrix resin is infused rapidly without requiring laying-up and shape-providing operations on the molding tool
Specifically, for example, in U.S. Pat. No. 5,071,711 and JP 4-26180 A, there is proposed a technique that a surface of a reinforcing fiber substrate is provided with a thermoplastic-like resin or a thermosetting resin, after being laid up in a shaping mold of a given shape, the resin is melt to thermally bond the interlayer of the reinforcing fiber substrate, cooled and solidified to form a preform retained in a given shape. According to these proposals, it is possible to obtain a preform excellent in shape retention by deforming a reinforcing fiber substrate in a given shape and bonding the interlayer.
However, according to these methods, there is an adverse effect that by sticking a resin component onto the surface of a reinforcing fiber substrate before forming a preform, rigidity of the reinforcing fiber substrate becomes strong, deformability is lowered and a shape-following property is deteriorated. Namely, in the case of trying to be deformed into a three-dimensional shape, a reinforcing fiber substrate cannot follow the shape and wrinkle occurs, as a result, the wrinkle of the reinforcing fiber substrate appears on the surface of the molded component obtained by impregnating and curing a matrix resin, which is inferior in the designing property as a commercial product. Besides, there are problems that impregnation deficiency takes place resulting from the wrinkle part occurred in a reinforcing fiber substrate upon infusing a matrix resin, further, the reinforcing fiber substrate is folded or broken at the wrinkle part, thereby the mechanical properties are deteriorated. This phenomenon is particularly notable in the case of using a method that imposes a reinforcing fiber substrate on a shaping mold for providing a shape in order to produce a three-dimensional shape with a large concavity and convexity.
From these facts, it has been strongly desired to provide a reinforcing fiber substrate having an excellent deformability capable of following a complicated shape without generating wrinkle in providing a shape as well as it has an excellent shape retention after providing the shape.
It could therefore be helpful to provide a reinforcing woven fabric having an excellent deformability capable of following a complicated shape and also is excellent in retention of the shape, a preform using it, a fiber reinforced plastic molded component using it, and a process for producing them, thereby to improve the productivity of the fiber reinforced plastic molded component.